The present invention relates to transmission networks of the type wherein a plurality of transmitters are transmitting streams of data frames over a broadband channel to a plurality of receivers, and relates particularly to a data transmission system using an orthogonal mapping of blocks and data streams into packets.
Today""s communication systems are capable of providing digital communication over a broadband channel at data rates far exceeding 30 Mbits/s. The frames of data transmitted over such a channel are typically of fixed length. Interface devices provided at the receiving end of the channel collect the transmitted data frames, then forward these frames to a destination computer where they are then converted into logical blocks of data for use by the computer""s software applications. An illustration of this method of transmission is the TCP/IP architecture used to transmit data over the Internet, in which the frames received by an interface device are encapsulated into IP packets which are then utilized by TCP/IP applications.
One disadvantage of this type of transmission system is the inability of today""s interface devices to independently process frame data. Current interface devices must interrupt the destination computer each time a frame is received so that its software can convert these frames into useful logical blocks of data. Such direct handling of frame data by the computer""s software has proven to be an inefficient use of CPU time. Thus, there is a need to translate frame data into useful data blocks directly within the network interface to improve the communication system described, in order to relieve the computer of this inefficient task of frame conversion.
Another shortcoming of present day network interfaces is their inefficient support of multicast data reception. This inefficiency results from a limited capability in the network interface to filter hardware addresses. For example, to support the reception of multicast IP datagrams in an Ethernet environment, a network interface must be able to receive packets with addresses that correspond to a particular host""s set of IP group addresses. It is the function of the address filter to limit the multicast packets received by the network interface to only those packets having a valid destination address.
Unfortunately, the address filters of many current Ethernet network interfaces can only be configured to recognize a small number of hardware addresses, thus requiring the address filter to be disabled (or xe2x80x9copened upxe2x80x9d) whenever the number of addresses within a particular group exceeds the limits of the filter. This disabling of the address filter can result in the computer having to inefficiently process data packets not intended for reception by its corresponding network interface. Thus, expanding the function of current address filter technology so as to improve the overall multicast transmission efficiency would be a desirable enhancement to the communication system described above.
A final unfavorable characteristic of the above described communication system relates to the unsecured method in which unicast transmissions are presently carried out over the network. Typically, broadcast of these unicast messages requires that the hardware address of a receiving station be accessible to the public in order to enable address resolution. For example, in TCP/IP, an Address Resolution Protocol (ARP) is used to share hardware addresses between host computers. Each host computer associates an IP address with a corresponding hardware address so that it can be determined to which interface device the frame data is to be forwarded. This public exchange of hardware address information makes it possible for information to be wrongfully intercepted through the use of counterfeit receiver hardware. Thus, devising a method of address resolution, whereby the hardware address of the receiving station need not be publicly disclosed, would be desirable to improve unicast transmission security.
Accordingly, the main object of the invention is to provide a data transmission system, wherein multiple computers can communicate to one another over a broadband channel using transmitters and receivers, each of which exchanges logical blocks of data that are carried over the channel in streams of frames.
Another object of the invention is to provide a data transmission system of the above type, wherein each host computer is attached to the broadband channel by using an intermediary receiving device, said device having the task of transforming frame data into logical data blocks that are then processed by the host computer upon receiving an interrupt signal from the receiving device indicating that the logical data blocks have been stored in the computer memory.
Another object of the invention is to provide a data transmission system of the above type, wherein multicast address filtering capability is expanded using a block identifier located within the received data packet itself that can be both masked and pattern matched against group address templates available to the receiving device.
Another object of the invention is to provide a data transmission system of the above type, wherein during unicast data transmission, unicast addresses are not publicly broadcast over the network, such that only authorized transmitters and the intended receiver itself possess the unicast address.
Therefore, the invention relates to a data transmission system, wherein a first plurality of transmitters transmits data packets over a broadband channel to a second plurality of receivers, in which each transmitter provides a stream of fixed-length packets constructed from a stream of variable length data blocks, each possibly originating from a different source, said packets being multiplexed amongst the various transmitters prior to being transmitted over the broadband channel.
In the preferred embodiment; transmitted data blocks are distributed over one or several fixed length packets, each packet comprising a packet header, having a source identifier that identifies the transmitting source, and the transmitted data itself. The first packet of any given transmitted data block also contains a block identifier that identifies the block being transmitted.
The preferred embodiment also permits multiple transmitters to transmit data concurrently over the broadband channel so long as each transmitter sends packets in the sequence that corresponds to their order within the data block. The packets may be interleaved and multiplexed on the broadband channel, however, each receiver is responsible for identifying packets belonging to each source or transmitter using the source identifier and reformatting the packets received into data blocks using the block identifier. Thus, the receiver must be capable of filtering through multiple packets originating from different transmitters and transforming them back into data blocks.